Field of Invention
The invention relates to a voltage detection circuit and method thereof, and particularly relates to a zero-crossing voltage detection circuit and method thereof.
Description of Related Art
FIG. 1A and FIG. 1B illustrate a schematic diagram of a typical buck converter. The buck converter 100 comprises two switches 101 and 102, two capacitor 103 and 104 and an inductor 105, in which only one switch is turned on at any time. As shown in the FIG. 1A, when the switch 101 is turned on and the switch 102 is turned off, the inductor 105 is connected to the voltage source Vin. Therefore, the current is from the voltage source Vin to the load 106. Because the two terminals of the inductor 105 are positive voltage, the current is increased. When the switch 101 is turned off and the switch 102 is turned on, the inductor 105 is connected to the ground. Therefore, the current is from the ground to the load 106. Because the two terminals of the inductor 105 are negative voltage, the current is decreased. The energy stored in the inductor 105 is released to the load 106. In such a mode, the load 106 is a heavy load and the current of the inductor 105 is a positive current, which the mode is called as a continuous conduction mode (CCM). The phase voltage (Vphase) of the inductor 105 is less than zero. On the other hand, as shown in the FIG. 1B, when the switch 101 is turned off and the switch 102 is turned on and when the load 106 is a light load, the current of the inductor 105 is decreased. When the current is less than zero, the current is reversed. Therefore, the energy stored in the capacitor 104 is released. That is, the current is from the load 106 to the ground. Because the current in the inductor 105 is reduced to zero, such a mode is called as a discontinuous conduction mode (DCM). The phase voltage (Vphase) of the inductor 105 is larger than zero.
Typically, a zero-crossing voltage detection circuit is used to detect the phase voltage (Vphase) of the inductor 105 to determine the operation mode, i.e., either a continuous conduction mode (CCM) for a heavy load or a discontinuous conduction mode (DCM) for a light load, of the buck converter to process a corresponding control to save energy. FIG. 1C is a schematic diagram of a typical zero-crossing voltage detection circuit. A comparator 110 compares the phase voltage (Vphase) of the inductor 105 with a ground voltage (GND) to determine when the phase voltage (Vphase) was approaching the zero crossing of the ground voltage (GND) so as to determine a corresponding operation mode, i.e., a continuous conduction mode (CCM) for a heavy load or a discontinuous conduction mode (DCM) for a light load.
The typical zero-crossing voltage detection circuit directly compares the phase voltage (Vphase) of the inductor 105 with a ground voltage (GND) to determine the time point of zero crossing, such that the detection velocity is fast. However, the comparators had variations that limited the accuracy of the comparators. Moreover, because the phase voltage (Vphase) and the ground voltage (GND) are directly inputted to the comparator, once the phase voltage (Vphase) has noise, the noise reduces the accuracy of detection. Accordingly, it is desirable to have a zero-crossing voltage detection circuit that has improved accuracy and that more accurately detects the zero crossing of a signal.